Communication method and device of terminal in wireless communication system

ABSTRACT

Disclosed is a 5G or pre-5G communication system for supporting a data transmission rate higher than that of a 4G communication system such as LTE. A communication method of a terminal in a wireless communication system, which includes a first base station supporting first wireless communication and a second base station supporting second wireless communication, can comprise the steps of: performing data communication though the first wireless communication with the first base station; receiving, from the first or second base station, configuration information for second wireless communication connection; reporting, to the first or second base station, the result of measurement on at least one beamforming reference signal having been received from the second base station, on the basis of the configuration information; and establishing the second wireless communication connection with the second base station on the basis of the measurement result.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a U.S. National Stage application under 35 U.S.C. §371 of an International application number PCT/KR2016/009166, filed onAug. 19, 2016, which is based on and claimed priority of a Indian patentapplication number 4378/CHE/2015, filed on Aug. 21, 2015, in the IndianIntellectual Property Office, and claimed priority of a Korean patentapplication number 10-2016-0005486, filed on Jan. 15, 2016, in theKorean Intellectual Property Office, and claimed priority of anotherKorean patent application number 10-2016-0014963, filed on Feb. 5, 2016,in the Korean Intellectual Property Office Indian patent applicationnumber 201641011346, filed on Mar. 31, 2016, in the Indian IntellectualProperty Office, the entire disclosure of each of which is herebyincorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates to a communication method and apparatus ofa terminal in a 5^(th) generation (5G) wireless communication system.

BACKGROUND ART

In order to meet the increasing demand for wireless data traffic sincethe commercialization of 4^(th) generation (4G) communication systems,the development focus is on the 5^(th) generation (5G) or pre-5Gcommunication system. For this reason, the 5G or pre-5G communicationsystem is called a beyond 4G network communication system or postlong-term evolution (LTE) system.

Consideration is being given to implementing the 5G communication systemin millimeter wave (mmW) frequency bands (e.g., 60 GHz bands) toaccomplish higher data rates. In order to increase the propagationdistance by mitigating propagation loss in the 5G communication system,discussions are underway about various techniques such as beamforming,massive multiple-input multiple output (MIMO), full dimensional MIMO(FD-MIMO), array antenna, analog beamforming, and large-scale antenna.

Also, in order to enhance network performance of the 5G communicationsystem, developments are underway of various techniques such as evolvedsmall cell, advanced small cell, cloud radio access network (RAN),ultra-dense network, device-to-device (D2D) communication, wirelessbackhaul, moving network, cooperative communication, coordinatedmulti-points (COMP), and interference cancellation.

Furthermore, the ongoing research includes the use of hybrid frequencyshift keying (FSK) and quadrature amplitude modulation (QAM){FQAM} andsliding window superposition coding (SWSC) as advanced coding modulation(ACM), filter bank multi-carrier (FBMC), non-orthogonal multiple access(NOMA), and sparse code multiple access (SCMA).

Many discussions are underway concerning the initial access of aterminal in a 5G system.

DISCLOSURE OF INVENTION Technical Problem

The present invention provides a 5G network access method of a terminalin the course of data communication through a 4^(th) generation (4G)network in a wireless communication system supporting both 4G and 5G.

Also, the present invention provides an initial access method of aterminal to a 5G network for data communication.

Solution to Problem

In accordance with an aspect of the present invention, a communicationmethod of a terminal in a radio communication system including a firstbase station supporting a first radio communication and second basestation supporting a second radio communication includes performing datacommunication through the first radio communication with the first basestation, receiving configuration information for second radiocommunication connection from the first or second base station,reporting a measurement result on at least one beamform reference signalreceived from the second base station to the first or second basestation based on the configuration information, and configuring thesecond radio communication connection with the second base station basedon the measurement result.

In accordance with another aspect of the present invention, acommunication method of a first base station in a radio communicationsystem including the first base station supporting a first radiocommunication and a second base station supporting a second radiocommunication includes performing data communication with the terminalconnected through the first radio communication, transmitting to theterminal configuration information for a second radio communicationconnection, and receiving a measurement result from the terminal, themeasurement result being generated based on at least one beamformingreference signal transmitted by the second base station based on theconfiguration information.

In accordance with another aspect of the present invention, acommunication method of a second base station in a radio communicationsystem including a first base station supporting a first radiocommunication and the second base station supporting a second radiocommunication includes transmitting configuration information for asecond radio communication connection to a terminal performing datacommunication with the first base station through the first radiocommunication, receiving a measurement result generated in associationwith at least one beamforming reference signal based on theconfiguration information, and configuring the second radiocommunication connection to the terminal based on the measurementresult.

In accordance with another aspect of the present invention, a terminalin a radio communication system including a first base stationsupporting a first radio communication and a second base stationsupporting a second radio communication includes:

a transceiver configured to transmit/receive a signal and a processorconfigured to control to perform data communication through the firstradio communication with the first base station, to receiveconfiguration information for a second radio communication connectionfrom the first or second base station, to report a measurement result onat least one beamform reference signal received from the second basestation to the first or second base station based on the configurationinformation, and to configure the second radio communication connectionwith the second base station based on the measurement result.

In accordance with another aspect of the present invention, a first basestation in a radio communication system including the first base stationsupporting a first radio communication and a second base stationsupporting a second radio communication includes a transceiverconfigured to transmit/receive a signal and a processor configured toperform data communication with the terminal connected through the firstradio communication, to transmit configuration information for a secondradio communication connection to the terminal, and to receive ameasurement result from the terminal, the measurement result beinggenerated based on at least one beamforming reference signal transmittedby the second base station based on the configuration information.

In accordance with still another aspect of the present invention, asecond base station in a radio communication system including a firstbase station supporting a first radio communication and the second basestation supporting a second radio communication includes a transceiverconfigured to transmit/receive a signal and a processor configured totransmit configuration information for a second radio communicationconnection to a terminal performing data communication with the firstbase station through the first radio communication, receive ameasurement result generated in association with at least onebeamforming reference signal based on the configuration information, andconfigure the second radio communication connection to the terminalbased on the measurement result.

Advantageous Effects of Invention

The present invention is advantageous in terms of facilitating 5Gnetwork access of a terminal connected to a 4G network. Also, thepresent invention is advantageous in terms of facilitating initialaccess of a terminal to a 5G network.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram illustrating a wireless communicationsupporting 4G and 5G;

FIG. 2 is a signal flow diagram illustrating an initial access procedureof a UE in a 5G system according to an embodiment of the presentinvention;

FIG. 3A is a signal flow diagram illustrating an initial accessprocedure of a UE in a 5G system according to another embodiment of thepresent invention;

FIG. 3B is a signal flow diagram illustrating an initial accessprocedure of a UE in a 5G system according to another embodiment of thepresent invention;

FIG. 4 is a signal flow diagram illustrating a connection releaseprocedure of a UE in a 5G system according to an embodiment of thepresent invention;

FIG. 5 is a signal flow diagram illustrating an initial access procedureof a UE in a 5G system according to another embodiment of the presentinvention;

FIG. 6 is a signal flow diagram illustrating a connection releaseprocedure of a UE in a 5G system according to another embodiment of thepresent invention;

FIG. 7 is a block diagram illustrating a schematic configuration of a UEaccording to an embodiment of the present invention;

FIG. 8 is a block diagram illustrating a schematic configuration of aneNB according to an embodiment of the present invention;

FIG. 9 is a block diagram illustrating a configuration of an internaldevice for turning on a 5G modem based on 5G application listinformation in a UE according to an embodiment of the present invention;

FIG. 10 is a block diagram illustrating a configuration of an internaldevice for turning on a 5G modem based on 5G application listinformation in a UE according to another embodiment of the presentinvention;

FIG. 11 is a diagram illustrating a situation where a UE located withina coverage of the master eNB is connected to the master eNB and asecondary eNB according to an embodiment of the present invention;

FIG. 12 is a signal flow diagram illustrating a procedure where a macroeNB triggers secondary cell search and measurement based on UE contextreceived from an MME after a UE has requested to the macro eNB forconnection;

FIG. 13 is a signal flow diagram illustrating a procedure where a macroeNB triggers secondary cell search and measurement based on apredetermined type of data from the network after a UE has connected tothe macro eNB;

FIG. 14 is a signal flow diagram illustrating a procedure where a macroeNB triggers secondary cell search and measurement based on apredetermined type of uplink data from a UE connected to the macro eNB;

FIG. 15 is a signal flow diagram illustrating a procedure where a UEtriggers secondary cell search and measurement based on a predeterminedtype of uplink data occurring at the UE after being connected to a macroeNB;

FIG. 16 is signal flow diagram illustrating a procedure where a UEtriggers secondary cell search and measurement based on a predeterminedtype of uplink data occurring at the UE in the idle state;

FIG. 17 is a signal flow diagram illustrating a procedure where a UE inthe idle state triggers secondary cell search and measurement based on apaging message indicative of the presence of downlink data;

FIG. 18 is a signal flow diagram illustrating a procedure for a UE inthe idle state to trigger a multiple secondary cell search procedure andmeasurement based on a paging message indicative of the presence ofdownlink data according to an embodiment of the present invention;

FIG. 19 is a signal flow diagram illustrating a procedure where an eNBtriggers secondary cell search and measurement based on the presence ofuplink data from a UE in the idle state;

FIG. 20 is a diagram for explaining a high frequency cell search andmeasurement method based on beamforming according to an embodiment ofthe present invention;

FIG. 21 is a block diagram illustrating a schematic configuration of aUE according to an embodiment of the present invention; and

FIG. 22 is a block diagram illustrating a schematic configuration of aneNB according to an embodiment of the present invention.

MODE FOR THE INVENTION

Exemplary embodiments of the present invention are described in detailwith reference to the accompanying drawings. Detailed descriptions ofwell-known functions and structures incorporated herein may be omittedto avoid obscuring the subject matter of the present invention. Further,the following terms are defined in consideration of the functionality inthe present invention, and they may vary according to the intention of auser or an operator, usage, etc. Therefore, the definition should bemade on the basis of the overall content of the present specification.

Before undertaking the detailed description of the present inventionbelow, it may be advantageous to set forth definitions of certain wordsand phrases used throughout the specification. However, it should benoted that the words and phrases are not limited to the exemplaryinterpretations herein.

In reference to FIG. 1, a wireless communication system may include a 4Gbase station 100 (e.g., LTE eNB) and a 5G base station 105 for serving aterminal 110. The terminal 110 may include an LTE modem for supportingLTE communication and a 5G modem for supporting 5G communication andperform data communication with a server through at least one of 4G and5G communication networks.

In the following description, the term “4G communication” may beinterchangeably referred to as “LTE communication” and “first radiocommunication,” and the term “5G communication” may be interchangeablyreferred to as “second radio communication.” In the followingdescription, the term “non-standalone system” may denote a wirelesscommunication system capable of providing both the 4G and 5G services,and the term “standalone system” may denotes a wireless communicationsystem capable of providing only the 5G service. According to anembodiment of the present invention, the terminal may perform an accessprocedure to the 4G network via the LTE eNB and transmit 5G capabilityinformation of the terminal to the LTE eNB or the 5G base station in the5G initial access procedure in the proposed non-standalone system. The5G capability information of the terminal may be conveyed in theterminal subscription information (e.g., international mobile equipmentidentity (IMEI)) and aggregate maximum bitrate (AMBR). Uponidentification of the 5G-capable terminal, the LTE eNB or the 5G basestation may transmit 5G cell configuration information and 5G cellmeasurement configuration information to the terminal. The terminal maytransmit to the base station the 5G radio capability information (e.g.,supportable carrier aggregation configuration, supportable MIMOconfiguration, and supportable beamforming configuration).

The terminal may perform 5G cell measurement based on the 5G cellconfiguration information and 5G cell measurement configurationinformation and transmit the 5G cell measurement result to the 5G basestation. The 5G base station may transmit the 5G base stationinformation for use by the terminal in accessing the 5G system based onthe 5G cell measurement result of the terminal. The 5G base station andgateway may configure a 5G data bearer for providing the terminal with a5G service. Afterward, the 5G base station may provide the terminal withthe 5G service through the 5G data bearer.

Hereinafter, a description is made of the 5G initial access procedure ofa terminal in a non-standalone system with reference to FIGS. 2, 3A, and3B.

FIG. 2 is a signal flow diagram illustrating a 5G initial accessprocedure of a terminal in a non-standalone system according to anembodiment of the present invention. In FIG. 2, the user equipment (UE)201 denotes a terminal, and the LTE eNB 203 denotes an LTE base station.The 5G access unit 1 (AU1) 205 and AU2 207 are network entities havingphysical (PHY) layer functions and some media access control (MAC) layerfunctions of a 5G eNB, and the 5G control unit (CU) 209 is an entityhaving the remaining functions (MAC, radio link control (RLC), packetdata convergence protocol (PDCP), and radio resource control (RRC)) withthe exception of the functions of the 5G AU. The 5G AU may be defined asa radio unit of the 5G eNB, and the 5G CU may be defined as a controlunit of the 5G eNB. The 5G AU and 5G CU may be configured to havefunctions different from the aforementioned functions, and detaileddescriptions on the functions of the 5G AC and 5G CU are omitted hereinbecause those are out of the scope of the present invention. The 5G eNBmay be separated into a 5G AU and a 5G CU or implemented as a singleentity. In the case that the 5G eNB is separated into two entities, the5G AU and 5G CU may be connected through an interface. The followingdescription is directed to the case where the 5G eNB is separated intothe 5G AU and 5G CU for convenience of explanation. However, the presentinvention is not limited thereto, and it includes embodiments in whichthe 5G eNB is a single entity without being separated into two entities.

If the UE 201 powers on, the LTE modem and the 5G modem are activated atsteps 221 and 223 and accesses to an LTE system via the LTE eNB 203according to a legacy procedure at step 225. Among the UEs connected tothe LTE system, the UE 201 having a 5G modem may receive a 5G RRCConnection information (configuration information necessary forestablishing a 5G RRC connection) as follows at step 227.

1) UE Initiated Triggering Via LTE eNB

The UE 201 with the 5G modem may notify the LTE eNB 203 of its 5Gcapability using the UE capability information that is transmitted inthe LTE initial access procedure. The UE 201 may transmit aUECapabilityInformation message including 5G capability in response to aUECapabilityEnquiry message. The UECapabilityInformation message mayinclude the information indicating whether the UE 201 supports the 5Gstandalone mode or 5G non-standalone mode. If the 5G capabilityinformation of the UE 201 is received, the LTE eNB 203 may transmit tothe 5G CU 209 a signal instructing generation of 5G RRC Connectioninformation or the 5G RRC Connection information may be generatedautonomously. If the 5G CU 209 or the LTE eNB 203 receives the signalinstructing generation of the 5G RRC Connection information, the 5G RRCConnection information may be generated and transmitted to the UE 201 atstep 229. The 5G RRC Connection information may include advanceinformation for use by the UE 201 in accessing the 5G AU/CU.

According to an embodiment of the present invention, the 5G RRCConnection information message may include at least one of 5G systeminformation (e.g., whole or part of 5G system information correspondingto LTE master information block (MIB) or system information blocks(SIBs)), 5G cell information (frequency, bandwidth, etc.), and 5G cellmeasurement configuration information. The 5G RRC Connection informationmessage may include a system frame number (SFN) parameter for use by the5G eNB. The 5G RRC Connection information may also include theinformation on one or more 5G AUs 205 and 207 being controlled by the 5GCU 209. The 5G RRC Connection information may also include theinformation (PHY, MAC, RLC, RRC, and PDCP information) necessary whenthe UE 201 communicates with the 5G CU 209/5G AUs 205 and 207. Forexample, the RRC information may include a C-RNTI for use in identifyingthe UE. In response to the 5G RRC Connection information message, the UE201 may transmit a 5G RRC Connection information ACK at step 231.

Meanwhile, the UE may search for the 5G AUs 205 and 207 using the 5G RRCConnection information. The 5G RRC Connection information may include 5GAU location information. The 5G AU location information may include atleast one of latitude and longitude of the locations of the 5G AUs 205and 207 and a radius thereof. The UE 201 may compare the correspondinginformation and its location information to determine whether to turnon/off the 5G modem and search for the 5G eNB. This makes it possible tosave power by protecting against any unnecessary 5G cell search andmeasurement operation. Alternatively, the UE may transmit its locationinformation to the 5G CU 209 periodically in order for the 5G CU 209 todetect the presence of the 5G AUs 205 and 207 around the UE. When the UE201 is located close to the 5G AU, the 5G CU 209 may transmit the 5G RRCConnection information.

2) UE Initiated Triggering Via 5G CU (RRC)

Among the UEs that have completed initial access to the LTE system, theUE having 5G capability may transmit a 5G RRC Connection informationrequest message to the 5G CU 209 via the LTE eNB 203. If the 5G CU 209is within the LTE service area, the 5G CU 209 may transmit a 5G RRCConnection information message at step 229 in response to the 5G RRCConnection information request message. Upon receipt of the 5G RRCConnection information message, the UE 201 may transmit a 5G RRCConnection information ACK message at step 231. If no 5G RRC Connectioninformation message is received after transmitting the 5G RRC Connectioninformation request message, the UE 201 may determine that there is no5G eNB within the current LTE service area. The LTE eNB 203 may transmitto the UE a message indicative of the absence of a 5G eNB.

According to an embodiment of the present invention, the 5G RRCConnection information message may include at least one of 5G systeminformation (e.g., whole or part of 5G system information correspondingto LTE master information block (MIB) or system information block(SIB)), 5G cell information (frequency, bandwidth, etc.), and 5G cellmeasurement configuration information. The 5G RRC Connection informationmessage may include an SFN parameter for use by the 5G eNB. The 5G RRCConnection information may also include the information on one or more5G AUs 205 and 207 being controlled by the 5G CU 209. The 5G RRCConnection information may also include the information (PHY, MAC, RLC,RRC, and PDCP information) necessary when the UE 201 communicates withthe 5G CU 209/5G AUs 205 and 207. For example, the RRC information mayinclude a C-RNTI for use in identifying the UE. In response to the 5GRRC Connection information message, the UE 201 may transmit a 5G RRCConnection information ACK at step 231.

The UE may search for the 5G AUs 205 and 207 using the 5G RRC Connectioninformation. The 5G RRC Connection information may include 5G AUlocation information. The 5G AU location information may include atleast one of latitude and longitude of the locations of the 5G AUs 205and 207 and a radius thereof The UE 201 may compare the correspondinginformation and its location information to determine whether to turnon/off the 5G modem and search for the 5G eNB. This makes it possible tosave power by protecting against any unnecessary 5G cell search andmeasurement operation.

3) LTE eNB Initiated Triggering

The LTE eNB 203 may check for the presence of the 5G CU 209 and the 5GAUs 205 and 207 within its transmission range. If the 5G CU 209 and the5G AUs 205 and 207 are within the transmission range of the LTE eNB 203,the UE may attempt initial access as follows.

The user information indicative of the 5G capability of the UE may bestored in the core network (e.g., home subscriber server (HSS)) in theform of an LTE system subscriber profile. The user information may beconveyed in an IMEI or AMBR parameter. If the IMEI or AMBR is set to avalue indicative of 5G, the MME 213 may transmit to the LTE eNB 203 theinformation indicating that the UE 201 supports 5G communication. Thismay be the case, for example, when the AMBR is set to a value greaterthan that for 4G communication and when the IMEI is set to a 5G-specificvalue. On the basis of the 5G capability information of the UE that isexchanged between the MME 213 and the LTE eNB 203, it may be possible toestablish an S1 or S5 bearer supporting 5G services. For example, theMME 213 may transmit to the LTE eNB 203 the information indicating thatthe UE 201 supports 5G communication. If the 5G capability informationof the UE 201 is received, the LTE eNB 203 may transmit a signalinstructing generation of 5G RRC Connection information or the 5G RRCConnection information may be generated autonomously.

If the 5G CU 209 or the LTE eNB 203 receives the signal instructinggeneration of the 5G RRC Connection information, the 5G RRC Connectioninformation may be generated and transmitted to the UE 201 at step 229.The 5G RRC Connection information may include advance information foruse by the UE 201 in accessing the 5G AU/CU.

According to an embodiment of the present invention, the 5G RRCConnection information message may include at least one of 5G systeminformation (e.g., whole or part of 5G system information correspondingto LTE MIB or SIBs), 5G cell information (frequency, bandwidth, etc.),and 5G cell measurement configuration information. The 5G RRC Connectioninformation message may include a system frame number (SFN) parameterfor use by the 5G eNB. The 5G RRC Connection information may alsoinclude the information on one or more 5G AUs 205 and 207 beingcontrolled by the 5G CU 209. The 5G RRC Connection information may alsoinclude the information (PHY, MAC, RLC, RRC, and PDCP information)necessary when the UE 201 communicates with the 5G CU 209/5G AUs 205 and207. For example, the RRC information may include a C-RNTI for use inidentifying the UE. In response to the 5G RRC Connection informationmessage, the UE 201 may transmit a 5G RRC Connection information ACK atstep 231. It may also be possible for the UE to search for the 5G AUs205 and 207 using the 5G RRC Connection information.

Alternatively, the LTE eNB 203 may check for the presence of the 5G CU209 and the 5G AUs 205 and 207 within its transmission range. If the 5GCU 209 and the 5G AUs 205 and 207 are within the transmission range ofthe LTE eNB 203 and the UE is attempting initial access, the LTE eNB 203may transmit to the 5G CU a signal instructing the 5G CU 209 to generate5G RRC Connection information or transmit the 5G RRC Connectioninformation to the 5G CU 209. The 5G CU 209 or the LTE eNB 203 maygenerate the 5G RRC Connection information and transmit the 5G RRCConnection information to the UE. If the UE 201 that has received thisinformation has 5G capability, it may transmit a 5G RRC Connectioninformation ACK at step 231. If the UE 201 that has received thisinformation has no 5G capability, the UE 201 may ignore the 5G RRCConnection information.

According to an embodiment of the present invention, the 5G RRCConnection information message may include at least one of 5G systeminformation (e.g., whole or part of 5G system information correspondingto LTE MIB or SIBs), 5G cell information (frequency, bandwidth, etc.)and 5G cell measurement configuration information. The 5G RRC Connectioninformation message may include a system frame number (SFN) parameterfor use by the 5G eNB. The 5G RRC Connection information may alsoinclude the information on one or more 5G AUs 205 and 207 beingcontrolled by the 5G CU 209. The 5G RRC Connection information may alsoinclude the information (PHY, MAC, RLC, RRC, and PDCP information)necessary when the UE 201 communicates with the 5G CU 209/5G AUs 205 and207. For example, the RRC information may include a C-RNTI for use inidentifying the UE. In response to the 5G RRC Connection informationmessage, the UE 201 may transmit a 5G RRC Connection information ACK atstep 231.

Meanwhile, the UE may search for the 5G AUs 205 and 207 using the 5G RRCConnection information. The 5G RRC Connection information may include 5GAU location information. The 5G AU location information may include atleast one of latitude and longitude of the locations of the 5G AUs 205and 207 and a radius thereof The UE 201 may compare the correspondinginformation and its location information to determine whether to turnon/off the 5G modem and search for the 5G eNB. This makes it possible tosave power by protecting against any unnecessary 5G cell search andmeasurement operation.

The 5G RRC Connection information may be acquired before or after the UE201 turns on the 5G modem. The UE 201 may store the 5G RRC Connectioninformation conveyed in the 5G RRC Connection information message foruse in configuring a 5G RRC connection.

The UE 201 may transmit 5G radio capability information (e.g.,supportable carrier aggregation configuration, supportable MIMOconfiguration, and supportable beamforming configuration) to the LTE eNBor the 5G eNB.

The 5G UE 201 may receive a synchronization signal (SS) (or SS/broadcastchannel (BCH) signal) to search for the 5G AUs 205 and 207 at steps 233and 235. If the SS (or SS/BCH signal) is received, the UE achievesdownlink synchronization. After achieving synchronization, the UE 201receives a BMRS to perform 5G AU measurement at step 237.

Alternatively, the UE may achieve synchronization based on the SS andthen receive the BMRS immediately to perform measurement.

Alternatively, the UE may achieve synchronization based on the BMRS andperform measurement immediately.

According to an embodiment of the present invention, the SS may includea 5G cell identifier. Alternatively, the BMRS may include a 5G cellidentifier.

If it is determined that communication is possible via a specific 5G AUas a result of measurement on the BMRS from the 5G AUs 205 and 207, theUE 201 may transmit a 5G Measurement report to the 5G CU 209 via the LTEeNB 203 at step 239. Alternatively, the UE 201 may transmit the 5GMeasurement report to the LTE eNB 203, and the LTE eNB 203 may deliverthe 5G Measurement report to the 5G CU 209. According to an embodimentof the present invention, the 5G Measurement report may include at leastone of 5G AU ID and BMRS measurement value (RSRP or RSRQ). The 5GMeasurement report may include the best downlink beam ID of available 5GAUs.

Upon receipt of the 5G Measurement report, the 5G CU 209 may select atstep 241 one 5G AU with the best measurement value or one or more 5G AUswith a measurement value equal to or greater than a predeterminedthreshold. FIG. 2 exemplifies a case where the 5G AU1 205 and 5G AU2 207are selected. It may be exemplified that the 5G AU1 205 is a serving(active) cell and the 5G AU2 207 is a candidate cell.

After selecting the 5G AU, the 5G CU 209 may transmit to the UE 201 atstep 243 a 5G RRC Connection Reconfiguration message includinginformation necessary for communication with a specific 5G AU. Thisinformation may include at least one of UE dedicated information, RNTI,Cell common information, Data Radio Bearer information, Dedicated RACHpreamble, and Dedicated RACH resource. The 5G RRC ConnectionReconfiguration message may include an SFN parameter for use by the 5GeNB.

After receiving the 5G Connection Reconfiguration message, the UE 201may transmit a 5G RRC Connection Reconfiguration Complete message to the5G CU 209 at step 245. Upon receipt of the 5G RRC ConnectionReconfiguration Complete message, the 5G CU 209 may transmit the 5G RRCConnection Reconfiguration message to the LTE eNB 203 at step 247. Uponreceipt of the 5G RRC Connection Reconfiguration Complete message, theLTE eNB 203 may perform data path switching to the 5G eNB (e.g. 5G AU1205) at step 249.

If the UE 201 receives the 5G RRC Connection Reconfiguration message, itmay transmit, at step 251, to the 5G AU1 205 a dedicated RACH preambleconveyed in the 5G RRC Connection Reconfiguration message. Here, the UE201 may transmit a dedicated RACH preamble on the beam selected as thebest reception beam, as a result of measurement on BMRS of thecorresponding AU 205, in two ways as follows.

1) Transmitting Measurement Report with Best Downlink Beam ID

For example, the UE 201 may transmit a dedicated RACH preamble on thebeam selected as the best reception beam once as a result of measurementon the BMRS of the corresponding AU 205. Suppose that the UE 201 selectsbeam 7 as the best downlink transmission beam and beam 3 as the bestuplink transmission beam as a result of measurement on BMRS of thecorresponding AU 205, then the UE 201 may transmit a measurement reportincluding the best downlink transmission beam ID 7. The 5G AU 205becomes aware that the best transmission beam for the UE 201 is beam 7and then receives the RACH preamble once on the beam 7 based on channelreciprocity. Since the best reception beam is beam 3, the UE 201 maytransmit the dedicated RACH preamble once on beam 3 based on channelreciprocity.

2) Transmitting Measurement Report without Best Downlink Beam ID

The UE 201 may transmit a dedicated RACH preamble N times on the bestreception beam 3, and the 5G AU1 205 may receive the dedicated RACHpreamble using beam sweeping. Here, N denotes a number of beams of the5G eNB. If the 5G AU 205 becomes aware of the best beam for the RACH, itmay also determine the best downlink beam using channel reciprocity.

Upon receipt of the dedicated RACH preamble, the 5G AU1 205 may checkfor the uplink timing of the UE and notify the UE of the uplink timingby transmitting a Random Access Response message at step 253. The RandomAccess Response message may include an SFN parameter for use by the 5GeNB.

According to an embodiment of the present invention, a contention-basedRACH preamble may be used instead of the dedicated RACH preamble. Inthis case, the UE may transmit an RACH preamble randomly selected froman RACH preamble set. If collision occurs, it may be possible toreattempt RACH preamble transmission through a backoff procedure. Ifaccess fails with a dedicated RACH preamble, the UE 201 may transmit acontention-based RACH preamble.

If a Random Access Response is received successfully from the 5G AU1 205in response to the contention-based RACH, the UE 201 may notify the 5GCU 209 of the successful RACH procedure via the LTE eNB 203.

The above-described initial access procedure may be applicable to ascenario where both the LTE modem and 5G modem are turned on when theterminal powers on.

It may also be possible to consider a scenario of performing the initialaccess procedure using a condition for the UE to turn on the 5G modem.

The scenarios for a UE to turn on the 5G modem based on a predeterminedcondition to perform the 5G initial access procedure in a non-standalonesystem may be categorized into two scenarios. The first scenario is toperform an application-based 5G initial access procedure, and the secondscenario is to perform an LTE eNB buffer status-based 5G initial accessprocedure.

FIG. 3A is a signal flow diagram illustrating an application-based 5Ginitial access procedure of a UE in a non-standalone system according toan embodiment of the present invention. In FIG. 3A, the UE 301 denotes aterminal, and the LTE eNB 303 denotes an LTE base station. The 5G AU1305 and 5G AU2 307 are network entities having PHY layer functions andMAC layer functions (e.g., HARQ) of a 5G eNB, and the 5G CU 309 is anetwork entity having the remaining functions (MAC, RLC, PDCP, and RRC)with the exception of the functions of the 5G AU. The 5G AUs 305 and 307and the 5G CU may be configured to have functions different form theaforementioned functions, and detailed descriptions on the functions ofthe 5G ACs 305 and 307 and the 5G CU 309 are omitted herein becausethose are out of the scope of the present invention. The 5G eNB may beseparated into a 5G AU and a 5G CU or implemented as a single entity. Inthe case that the 5G eNB is separated into two entities, the 5G AU and5G CU may be connected through an interface. The following descriptionis directed to the case where the 5G eNB is separated into the 5G AU and5G CU for convenience of explanation. However, the present invention isnot limited thereto, and it includes embodiments in which the 5G eNB isa single entity without being separated into two entities.

If the UE 301 powers on at step 321, the LTE modem is activated at step323 to access to an LTE system via the LTE eNB 303 at step 325 accordingto a legacy procedure. Among the UEs connected to the LTE system, the UE301 having a 5G modem may receive a 5G RRC Connection information(configuration information necessary for establishing a 5G RRCconnection) at step 325 as follows.

1) UE Initiated Triggering Via LTE eNB

The UE 301 with the 5G modem may notify the LTE eNB 303 of its 5Gcapability using the UE capability information that is transmitted inthe LTE initial access procedure. The UE 301 may transmit aUECapabilityInformation message including 5G capability in response to aUECapabilityEnquiry message. The UECapabilityInformation message mayinclude the information indicating whether the UE 301 supports the 5Gstandalone mode or 5G non-standalone mode. If the 5G capabilityinformation of the UE 301 is received, the LTE eNB 303 may transmit tothe 5G CU 309 a signal instructing generation of 5G RRC Connectioninformation or the 5G RRC Connection information may be generatedautonomously. If the 5G CU 309 or the LTE eNB 303 receives the signalinstructing generation of the 5G RRC Connection information, the 5G RRCConnection information may be generated and transmitted to the UE 201 atstep 327. The 5G RRC Connection information may include advanceinformation for use by the UE 301 in accessing the 5G AU/CU.

According to an embodiment of the present invention, the 5G RRCConnection information message may include at least one of 5G systeminformation (e.g., whole or part of 5G system information correspondingto LTE MIB or SIBs), 5G cell information (frequency, bandwidth, etc.),and 5G cell measurement configuration information. The 5G RRC Connectioninformation message may include an SFN parameter for use by the 5G eNB.The 5G RRC Connection information may also include the information onone or more 5G AUs 305 and 307 being controlled by the 5G CU 309. The 5GRRC Connection information may also include the information (PHY, MAC,RLC, RRC, and PDCP information) necessary when the UE 301 communicateswith the 5G CU 309/5G AUs 305 and 307. For example, the RRC informationmay include a C-RNTI for use in identifying the UE. In response to the5G RRC Connection information message, the UE 301 may transmit a 5G RRCConnection information ACK at step 329.

Meanwhile, the UE may search for the 5G AUs 305 and 307 using the 5G RRCConnection information. The 5G RRC Connection information may include 5GAU location information. The 5G AU location information may include atleast one of latitude and longitude of the locations of the 5G AUs 305and 307 and a radius thereof. The UE 301 may compare the correspondinginformation and its location information to determine whether to turnon/off the 5G modem and search for the 5G eNB. This makes it possible tosave power by protecting against any unnecessary 5G cell search andmeasurement operation. Alternatively, the UE may transmit its locationinformation to the 5G CU 309 periodically in order for the 5G CU 309 todetect the presence of the 5G AUs 305 and 307 around the UE. When the UE301 is located close to the 5G AU, the 5G CU 309 may transmit the 5G RRCConnection information.

2) UE Initiated Triggering Via 5G CU (RRC)

Among the UEs that have completed initial access to the LTE system, theUE having the 5G capability may transmit a 5G RRC Connection informationrequest message to the 5G CU 309 via the LTE eNB 303. If the 5G CU 309is within the LTE service area, the 5G CU 309 may transmit a 5G RRCConnection information message at step 327 in response to the 5G RRCConnection information request message. Upon receipt of the 5G RRCConnection information message, the UE 301 may transmit a 5G RRCConnection information ACK message at step 329. If no 5G RRC Connectioninformation message is received after transmitting the 5G RRC Connectioninformation request message, the UE 301 may determine that there is no5G eNB within the current LTE service area. The LTE eNB 303 may transmitto the UE a message indicative of the absence of a 5G eNB.

The 5G RRC Connection information may include advance information foruse by the UE 301 in accessing the 5G AU/CU. According to an embodimentof the present invention, the 5G RRC Connection information message mayinclude at least one of 5G system information (e.g., whole or part of 5Gsystem information corresponding to LTE MIB or SIBs), 5G cellinformation (frequency, bandwidth, etc.), and 5G cell measurementconfiguration information. The 5G RRC Connection information message mayinclude an SFN parameter for use by the 5G eNB. The 5G RRC Connectioninformation may also include the information on one or more 5G AUs 305and 307 being controlled by the 5G CU 309. The 5G RRC Connectioninformation may also include the information (PHY, MAC, RLC, RRC, andPDCP information) necessary when the UE 301 communicates with the 5G CU309/5G AUs 305 and 307. For example, the RRC information may include aC-RNTI for use in identifying the UE. In response to the 5G RRCConnection information message, the UE 301 may transmit a 5G RRCConnection information ACK at step 329.

It may also be possible for the UE to search for the 5G AUs 305 and 307using the 5G RRC Connection information. The 5G RRC Connectioninformation may include 5G AU location information. The 5G AU locationinformation may include at least one of latitude and longitude of thelocation of the 5G AUs 305 and 307 and a radius. The UE 301 may comparethe corresponding information and its location information to determinewhether to turn on/off the 5G modem and search for the 5G eNB. Thismakes it possible to save power by protecting against any unnecessary 5Gcell search and measurement operation.

3) LTE eNB Initiated Triggering

The LTE eNB 303 may check for the presence of the 5G CU 309 and the 5GAUs 305 and 307 within its transmission range. If the 5G CU 309 and the5G AUs 305 and 307 are within the transmission range of the LTE eNB 303,the UE may attempt initial access as follows.

The user information indicative of the 5G capability of the UE may bestored in the core network (e.g., HSS) in the form of an LTE systemsubscriber profile. The user information may be conveyed in an IMEI orAMBR parameter. If the IMEI or AMBR is set to a value indicative of 5G,the MME 313 may transmit to the LTE eNB 303 the information indicatingthat the UE 301 supports 5G communication. This may be the case, forexample, when the AMBR is set to a value greater than that for 4Gcommunication and when the IMEI is set to a 5G-specific value. On thebasis of the 5G capability information of the UE that is exchangedbetween the MME 313 and the LTE eNB 303, it may be possible to establishan S1 or S5 bearer supporting 5G services. For example, the MME 313 maytransmit to the LTE eNB 303 the information indicating that the UE 301supports 5G communication. If the 5G capability information of the UE301 is received, the LTE eNB 303 may transmit a signal instructinggeneration of 5G RRC Connection information or the 5G RRC Connectioninformation may be generated autonomously.

If the 5G CU 309 or the LTE eNB 303 receives the signal instructinggeneration of the 5G RRC Connection information, the 5G RRC Connectioninformation may be generated and transmitted to the UE 301 at step 327.The 5G RRC Connection information may include advance information foruse by the UE 301 in accessing the 5G AU/CU.

According to an embodiment of the present invention, the 5G RRCConnection information message may include at least one of 5G systeminformation (e.g., whole or part of 5G system information correspondingto LTE MIB or SIBs), 5G cell information (frequency, bandwidth, etc.)and 5G cell measurement configuration information. The 5G RRC Connectioninformation message may include an SFN parameter for use by the 5G eNB.The 5G RRC Connection information may also include the information onone or more 5G AUs 305 and 307 being controlled by the 5G CU 309. The 5GRRC Connection information may also include the information (PHY, MAC,RLC, RRC, and PDCP information) necessary when the UE 301 communicateswith the 5G CU 309/5G AUs 305 and 307. For example, the RRC informationmay include a C-RNTI for use in identifying the UE. In response to the5G RRC Connection information message, the UE 301 may transmit a 5G RRCConnection information ACK at step 329. It may also be possible for theUE to search for the 5G AUs 305 and 307 using the 5G RRC Connectioninformation.

Alternatively, the LTE eNB 303 may check for the presence of the 5G CU309 and the 5G AUs 305 and 307 within its transmission range. If the 5GCU 309 and the 5G AUs 305 and 307 are within the transmission range ofthe LTE eNB 303 and if the UE is attempting initial access, the LTE eNB303 may transmit to the 5G CU a signal instructing the 5G CU 309 togenerate 5G RRC Connection information or transmit the 5G RRC Connectioninformation to the 5G CU 309. The 5G CU 309 or the LTE eNB 303 maygenerate the 5G RRC Connection information and transmit the 5G RRCConnection information to the UE at step 327. If the UE 301 that hasreceived this information has 5G capability, it may transmit a 5G RRCConnection information ACK at step 329. If the UE 301 that has receivedthis information has no 5G capability, the UE 301 may ignore the 5G RRCConnection information.

The 5G RRC Connection information may include advance information foruse by the UE 301 in accessing the 5G AUs 305 and 307. According to anembodiment of the present invention, the 5G RRC Connection informationmessage may include at least one of 5G system information (e.g., wholeor part of 5G system information corresponding to LTE MIB or SIBs), 5Gcell information (frequency, bandwidth, etc.), and 5G cell measurementconfiguration information. The 5G RRC Connection information message mayinclude an SFN parameter for use by the 5G eNB. The 5G RRC Connectioninformation may also include the information on one or more 5G AUs 305and 307 being controlled by the 5G CU 309. The 5G RRC Connectioninformation may also include the information (PHY, MAC, RLC, RRC, andPDCP information) necessary when the UE 301 communicates with the 5G CU309/5G AUs 305 and 307. For example, the RRC information may include aC-RNTI for use in identifying the UE. In response to the 5G RRCConnection information message, the UE 301 may transmit a 5G RRCConnection information ACK at step 329.

Meanwhile, the UE may search for the 5G AUs 305 and 307 using the 5G RRCConnection information. The 5G RRC Connection information may include 5GAU location information. The 5G AU location information may include atleast one of latitude and longitude of the locations of the 5G AUs 305and 307 and a radius thereof. The UE 301 may compare the correspondinginformation and its location information to determine whether to turnon/off the 5G modem and search for the 5G eNB. This makes it possible tosave power by protecting against any unnecessary 5G cell search andmeasurement operation.

The UE 301 may transmit 5G radio capability information (e.g.,supportable carrier aggregation configuration, supportable MIMOconfiguration, and supportable beamforming configuration) to the LTE eNBor the 5G eNB.

If a 5G application is executed at step 331, the 5G UE 301 may turn onthe 5G modem to perform the initial access procedure to the 5G eNB usingthe 5G RRC Connection information. It may be possible that the 5Gapplication information is sent to the 5G modem of the UE 301 throughthe application layer. Step 331 is described in detail later withreference to FIGS. 9 and 10. According to an embodiment of the presentinvention, the UE 301 may have a pre-configured 5G application list orreceive the 5G application list through the LTE system.

As the 5G modem of the UE 301 is turned on but does not have a 5Gconnection yet, the UE 301 may receive data through the LTE connectionat step 333. At this time, the UE 301 may receive a signal through adefault bearer established in the initial access procedure or set up adedicated bearer to receive 5G data.

After turning on the 5G modem, the 5G UE 301 may receive SS/BCH from the5G AUs 305 and 307 at steps 335 and 337 to achieve downlinksynchronization. After achieving synchronization, the UE 301 may receivea BMRS to perform 5G AU measurement at step 339. Alternatively, the UE301 may perform the measurement immediately after achievingsynchronization based on the BMRS. According to an embodiment of thepresent invention, the SS may include a 5G cell identifier.Alternatively, the BMRS may include the 5G cell identifier.

If it is determined that communication is possible via a specific 5G AUas a result of measurement on the BMRS from the 5G AUs 305 and 307, theUE 301 may transmit a 5G Measurement report to the 5G CU 309 via the LTEeNB 303 at step 341. Alternatively, the UE 201 may transmit the 5GMeasurement report to the LTE eNB 303, and the LTE eNB 303 may deliverthe 5G Measurement report to the 5G CU 309. According to an embodimentof the present invention, the 5G Measurement report may include at leastone of 5G AU ID and BMRS measurement value (RSRP or RSRQ). The 5GMeasurement report may include the best downlink beam ID of available 5GAUs.

Upon receipt of the 5G Measurement report, the 5G CU 309 may, at step343, select one 5G AU with the best measurement value or one or more 5GAUs with a measurement value equal to or greater than a predeterminedthreshold. FIG. 3A exemplifies a case where the 5G AU1 305 and 5G AU2307 are selected. It may be exemplified that the 5G AU1 305 is a serving(active) cell and the 5G AU2 307 is a candidate cell.

After selecting the 5G AU, the 5G CU 309 may transmit to the UE 301 atstep 345 a 5G RRC Connection Reconfiguration message includinginformation necessary for communication with a specific 5G AU. Thisinformation may include at least one of UE dedicated information, RNTI,Cell common information, Data Radio Bearer information, Dedicated RACHpreamble, and Dedicated RACH resource. The 5G RRC ConnectionReconfiguration message may include an SFN parameter for use by the 5GeNB.

After receiving the 5G Connection Reconfiguration message, the UE 301may transmit a 5G RRC Connection Reconfiguration Complete message to the5G CU 309 at step 347. Upon receipt of the 5G RRC ConnectionReconfiguration Complete message, the 5G CU 309 may transmit the 5G RRCConnection Reconfiguration message to the LTE eNB 303 at step 349. Uponreceipt of the 5G RRC Connection Reconfiguration Complete message, theLTE eNB 303 may transmit UE data accumulated in the buffer until then tothe 5G AU1 305 at step 351 and perform data path switching to the 5G eNB(e.g. 5G AU1 305) at step 357.

Meanwhile, if the UE 301 receives the 5G RRC Connection Reconfigurationmessage, it may transmit, at step 353, to the 5G AU1 305 a dedicatedRACH preamble conveyed in the 5G RRC Connection Reconfiguration message.Here, the UE 301 may transmit a dedicated RACH preamble on the beamselected as the best reception beam, as a result of measurement on BMRSof the corresponding AU 305, in two ways as follows.

1) Transmitting Measurement Report with Best Downlink Beam ID

For example, the UE 301 may transmit a dedicated RACH preamble on thebeam selected as the best reception beam once as a result of measurementon the BMRS of the corresponding AU 305. Suppose that the UE 301 selectsbeam 7 as the best downlink transmission beam and beam 3 as the bestuplink transmission beam as a result of measurement on BMRS of thecorresponding AU 305, then the UE 301 may transmit a measurement reportincluding the best downlink transmission beam ID 7. The 5G AU 305becomes aware that the best transmission beam for the UE 301 is beam 7and then receives the RACH preamble once on the beam 7 based on channelreciprocity. Since the best reception beam is beam 3, the UE 301 maytransmit the dedicated RACH preamble once on beam 3 based on channelreciprocity.

2) Transmitting Measurement Report without Best Downlink Beam ID

The UE 301 may transmit a dedicated RACH preamble N times on the bestreception beam 3, and the 5G AU1 305 may receive the dedicated RACHpreamble using beam sweeping. Here, N denotes a number of beams of the5G eNB. If the 5G AU1 305 becomes aware of the best beam for the RACH,it may also determine the best downlink beam using channel reciprocity.

Upon receipt of the dedicated RACH preamble, the 5G AU1 305 may checkfor the uplink timing of the UE and notify the UE of the uplink timingby transmitting a Random Access Response message at step 355. The RandomAccess Response message may include an SFN parameter for use by the 5GeNB.

According to an embodiment of the present invention, a contention-basedRACH preamble may be used instead of the dedicated RACH preamble. Inthis case, the UE may transmit an RACH preamble randomly selected froman RACH preamble set. If collision occurs, it may be possible toreattempt RACH preamble transmission through a backoff procedure. Ifaccess fails with a dedicated RACH preamble, the UE 301 may transmit acontention-based RACH preamble.

If a Random Access Response is received successfully from the 5G AU1 305in response to the contention-based RACH, the UE 301 may notify the 5GCU 309 of the successful RACH procedure via the LTE eNB 303.

FIG. 3B is a signal flow diagram illustrating an LTE eNB bufferstatus-based 5G initial access procedure of a UE in a non-standalonesystem according to an embodiment of the present invention. In FIG. 3B,the UE 301 denotes a terminal, and the LTE eNB 303 denotes an LTE basestation. The 5G AU1 305 and 5G AU2 307 are network entities having PHYlayer functions and MAC layer functions (e.g., HARQ) of a 5G eNB, andthe 5G CU 309 is a network entity having the remaining functions (MAC,RLC, PDCP, and RRC) with the exception of the functions of the 5G AU.The 5G eNB may be separated into a 5G AU and a 5G CU or implemented as asingle entity. In the case that the 5G eNB is separated into twoentities, the 5G AU and 5G CU may be connected through an interface. Thefollowing description is directed to the case where the 5G eNB isseparated into the 5G AU and 5G CU for convenience of explanation.However, the present invention is not limited thereto, and it includesembodiments in which the 5G eNB is a single entity without beingseparated into two entities.

The procedure of FIG. 3B is similar to that of FIG. 3A, but it hasdifferences as follows. If a 5G application is executed in the UE, theUE 301 may receive data via the LTE eNB 303 at step 371. If a largevolume of 5G data arrives at the LTE eNB 303 and it is detected at step373 that the data amount buffered in the LTE eNB buffer has becomegreater than a predetermined threshold because of the transmission limitof the LTE eNB 303, the LTE eNB 303 may transmit to the 5G CU 309 asignal instructing generation of 5G RRC Connection information. In thiscase, the 5G CU 309 may generate and transmit the 5G RRC Connectioninformation at step 375, or the LTE eNB 303 may autonomously generateand transmit the 5G RRC Connection information.

The 5G RRC Connection information may include advance information foruse by the UE 301 in accessing the 5G AU/CU. The 5G RRC Connectioninformation message may include at least one of 5G system information(e.g., whole or part of 5G system information corresponding to LTE MIBor SIBs), 5G cell information (frequency, bandwidth, etc.), and 5G cellmeasurement configuration information. The 5G RRC Connection informationmessage may include an SFN parameter for use by the 5G eNB. The 5G RRCConnection information may also include the information on one or more5G AUs 305 and 307 being controlled by the 5G CU 309. The 5G RRCConnection information may also include the information (PHY, MAC, RLC,RRC, and PDCP information) necessary when the UE 301 communicates withthe 5G CU 209/5G AUs 305 and 307. For example, the RRC information mayinclude a C-RNTI for use in identifying the UE.

In response to the 5G RRC Connection information message, the UE 301 maytransmit a 5G RRC Connection information ACK at step 379. The UE 301 maytransmit 5G radio capability information (e.g., supportable carrieraggregation configuration, supportable MIMO configuration, andsupportable beamforming configuration) to the LTE eNB or the 5G eNB. Theoperations of the subsequent steps may be performed in the same way asthose of the procedure of FIG. 3A.

If the 5G eNB capacity is saturated so as not to serve the UE 301, theeNB has to bar UE access to the eNB. The UE access barring notificationinformation may be conveyed in at least one of the 5G RRC Connectioninformation message, the 5G RRC Connection Reconfiguration message, andthe Random Access Response message. The UE access barring notificationinformation may include at least one of a UE access baring indicator, anaccessible UE class/type, and an access-retry available timing of theaccess-barred UE. If the UE 301 receives the UE access barringnotification information through the 5G RRC Connection informationmessage, the 5G RRC Connection Reconfiguration message, and the RandomAccess Response message, it may stop the procedure of accessing the 5GeNB. If the UE access barring notification information includes theaccess-retry available timing of the access-barred UE, the UE mayperform the 5G access procedure to the same 5G eNB at the access-retryavailable timing. It may also be possible for the UE 301 to try 5Gaccess to another 5G eNB rather than the access-barred 5G eNB. In orderto generate the UE access barring notification information, it may benecessary to exchange information between the LTE eNB and the 5G eNB.

FIG. 4 is a signal flow diagram illustrating signal flows in a procedureof terminating 5G connection in a non-standalone system according to anembodiment of the present invention. In reference to FIG. 4, the UE 401may receive 5G service data packets through 5G eNB/S-GW/P-GW at steps421 and 423. The service data packet transmission may be performed usinga beam selected in a beamforming procedure between the UE and the 5G eNB(e.g., 5G AU1 405). In the course of transmitting a signal including theservice data packet, the 5G eNB (e.g., 5G CU 409) may determine at step425 whether a 5G RRC release timer has expired. If the 5G RRC releasetimer expires, the 5G eNB (5G CU 409) may switch the data path for theUE 401 from the 5G AU1 405 to the LTE eNB 403 at step 427. Then, the eNB(5G CU 409) may release the radio context for the UE 401, e.g., RNTI, 5Gcell measurement configuration information, and DRX mode configurationinformation, at step 429. The eNB (5G CU 409) may transmit a 5G RRCConnection Release message to the UE 401 at step 431. After releasingthe 5G RRC Connection, the UE 401 may turn off the 5G modem or perform acell search procedure for searching for a 5G AU. It is obvious that theUE 401 may receive the service via the LTE system after turning off the5G modem.

As an alternative example of releasing system connection of the UE, theeNB (5G CU 409) may check the buffer status of the UE 401 to determinethat no 5G radio (5G system) is necessary for serving the UE 401. TheeNB (5G CU) 409 may perform the 5G RRC connection release procedure withthe S-GW 411, P-GW (not shown), and MME 413 and transmit a 5G RRCConnection Release message to the UE 401. If the 5G RRC ConnectionRelease message is received, the UE 401 may release the RRC context withthe 5G cell (eNB (5G CU 409)). The UE 401 may transmit a response to theeNB (5G CU 409) in response to the 5G RRC Connection Release message.Upon receipt of the response, the eNB (5G CU 409) may release the 5Gcontext (5G radio context) for the UE 401. After releasing the 5G RRCConnection, the UE 401 may turn off the 5G modem or perform a cellsearch procedure to search for a 5G AU. It is obvious that the UE 401may receive the service via the LTE system after turning off the 5Gmodem if it supports the LTE system.

As another alternative example of releasing system connection of the UE,the UE 401 may transmit an RRC Connection Release Request message to theeNB (5G CU 409), and the eNB (5G CU 409) may transmit an RRC ConnectionRelease Confirm message in reply. The UE 401 may operate an RRC contextrelease timer to transmit the RRC Connection Release Request message. Ifthe 5G communication service application is deactivated, the applicationprocessor (AP) of the UE 401 may generate a command instructing releaseof the RRC connection to its 5G modem, which may transmit the RRCConnection Release Request message. If the UE has the 5G eNB locationinformation, it may compare its location and the 5G eNB location and, ifthe UE is not located within the service area of the 5G eNB any more,transmit an RRC Connection Release Request message by means of the 5Gmodem. If the RRC Connection Release Request message is received fromthe UE 401, the eNB (5G CU 409) may perform a 5G RRC Connection releaseprocedure with the S-GW 411, P-GW (not shown), and MME 413 and transmita 5G RRC Connection Release message to the UE 401. If the 5G RRCConnection Release message is received, the UE 401 may release the RRCContext with the 5G cell (eNB (5G CU 409)). The eNB (5G CU 409) mayrelease the 5G context (5G radio context) for the UE 401. Afterreleasing the 5G RRC Connection, the UE 401 may turn off the 5G modem orperform a cell search procedure to search for a 5G AU.

FIG. 5 is a signal flow diagram illustrating signal flows between a UEand a system during a system access procedure in a standalone scenarioof a new system (e.g., 5G system) according to an embodiment of thepresent invention.

Here, examples of the legacy system include the LTE system andLTE-Advanced system, and examples of the new system include the 5Gsystem.

If the UE 501 powers on, the 5G modem turns on, and the UE operations tobe described hereinafter may be implemented by the 5G modem. The UE 501may search for a 5G cell and perform a procedure of accessing the systemthrough the 5G cell. If the system access procedure is completed, the UE501 may receive the communication service through the system. The basestation apparatus that manages the 5G cell may include a radio unit(e.g., 5G AU1 503 and 5G AU2 505) and a control unit (5G CU 507), whichmay be implemented as separate devices or as a single device. In thecase that the radio unit and the control unit are implemented asseparate devices, they may exchange signals through an interface. InFIG. 5, the radio unit and the control unit are depicted as separatedevices. It may not be necessary to differentiate between the radio unitand the control unit of the base station and, in the followingdescription, the radio unit and the control unit are referred to as basestation collectively.

A description is made of the procedure for a UE 501 to search for a 5Gcell and access the system through the 5G cell with reference to FIG. 5.Alternatively, in the case where the UE 501 has found both the 4G and 5Gcells, it may be possible to allow the UE 501 to refer to a cellselection priority (or cell reselection priority) as a metric forselecting a cell to perform a system access procedure, by assigningdifferent cell selection priorities to 4G and 5G cells. The prioritiesof the 4G and 5G cells may be set according to the subscribed service ofthe UE and management policy of the network operator.

In reference to FIG. 5, if the UE 501 powers on at step 521, it mayreceive synchronization reference signals (SS) from the 5G AU1 503 andthe 5G AU2 505 at steps 523 and 525. The UE 501 may search for 5G cellsbased on the SS and select a base station (i.e., 5G cell) at step 527 toperform the system access procedure. The UE 501 may achieve time andfrequency synchronization with the base station based on the SS. The UE501 may further receive a system information signal (PBCH) and beammeasurement reference signal (BMRS) transmitted by the base station (5GAU1 503 and 5G AU2 505). According to an embodiment of the presentinvention, the SS may include a 5G cell identifier. Alternatively, theBMRS may include the 5G cell identifier.

The PBCH may include system information (e.g., BMRS configuration,period, transmission position, and transmission resource) for receivingBMRS. The PBCH may also include basic system information (e.g., systemframe number, downlink channel configuration, and HARQ configuration)necessary to access the system via the base station in addition to thesystem information related to the BMRS. The UE 501 may acquire adownlink beam based on the BMRS. For example, the UE may performmeasurement on the BMRS to select the best downlink beam.

The UE may receive other system information (SIB1, SIB2, etc.)transmitted by the base station (5G AU1 503 and 5G AU2 505) at step 529.The other system information may include the information necessary forperforming an RACH procedure to the base station (e.g., RACH preamble,RACH resource position, and RACH resource period).

The UE 501 may perform the RACH procedure with the base station based onthe RACH information. The RACH procedure may be initiated bytransmitting an RACH preamble at step 531. The UE 501 may transmit theRACH preamble including the previously acquired best downlink beaminformation to the base station. At step 533, the UE 501 may receive aRandom Access Response from the base station in response to the RACHpreamble. The UE 501 may acquire uplink resource information necessaryfor transmitting timing advance (TA) information and an RRC ConnectionRequest message to the base station.

The UE 501 may transmit an RRC Connection Request message to the basestation at step 535 and receive an RRC Connection Setup message from thebase station at step 537 in response to RRC Connection Request message.The UE 501 may transmit 5G radio capability information (e.g.,supportable carrier aggregation configuration, supportable MIMOconfiguration, and supportable beamforming configuration) to the basestation.

If the UE 501 receives the RRC Connection Setup message at step 537, asignaling radio bearer 1 (SRB1) may be established between then UE 501and the base station. The UE 501 may transmit an RRC Connection SetupComplete message to the base station at step 539. At step 541, the UE501 may perform an EPS bearer setup procedure with a gateway and server(S/P-GW 509, MME 511, and server 513) for data communication.

If the EPS bearer is established for the UE 501, the UE 501 may receivean RRC Connection Reconfiguration message from the base station at step543. The RRC Connection Reconfiguration message may include at least oneof data radio bearer (DRB) information and 5G cell measurementconfiguration information. The 5G cell measurement configurationinformation may include at least one of 5G intra-frequency information,5G inter-frequency information, beam measurement reference signalinformation, and 5G cell measurement report triggering metricinformation. The RRC Connection Reconfiguration message may also includeDRX mode configuration information for 5G cell.

At step 545, the UE 501 may transmit an RRC Connection ReconfigurationComplete message in response to the RRC Connection Reconfigurationmessage. Afterward, the service starts at step 547, and the UE mayperform a service setup procedure at step 549 for receiving the servicethrough the established EPS bearer and DRB. A service request signalnecessary for triggering the service setup procedure may be transmittedto a service server 513 (e.g., youtube server) in the form of a datapacket. Here, the UE 501 may transmit/receive the service setup signalson the beam selected through the beamforming procedure (beam selection,beam tracking, and beam sweeping) with the base station. Aftercompleting the service setup procedure, the UE 501 may receive theservice provided by the service server 513 at step 551. The signalsconveying the service may be transmitted on the beam selected in thebeamforming procedure with the base station. The beamforming proceduremay be performed based on the beam measurement reference signaltransmitted by the base station as denoted by reference number 553.

FIG. 6 is a signal flow diagram illustrating signal flows between a UEand a system during a connection release procedure in a standalonescenario of a new system according to an embodiment of the presentinvention.

In reference to FIG. 6, the UE 601 may perform a service setup procedurefor receiving a service through the established EPS bearer and DRB atstep 621 and receive service data packets through the basestation/S-GW/P-GW at step 623. The service data packet transmission maybe performed using a beam selected in the beamforming procedure betweenthe UE 601 and the base station. The base station (5G CU 607) may detectthe expiry of the 5G RRC release timer at step 625 in the course oftransmitting a signal including the service data packet to the UE 601.If the 5G RRC release timer expires, the base station (5G CU 607) mayperform an RRC Connection release procedure with the S/P-GW 609 and MME611 at step 627 for releasing the RRC connection of the UE 601.

The base station (5G AU1 603) may release the radio context of the UE(e.g., RNTI, 5G cell measurement configuration information, and DRX modeconfiguration information) at step 629. The base station (5G AU1 603)may transmit a 5G RRC Connection Release message to the UE 601 at step631.

If the 5G RRC Connection Release message is received, the UE 601 mayrelease the RRC context related to the 5G cell (base station). The UE601 may transmit a response to the base station in response to the 5GRRC Connection Release message. Alternatively, the base station mayrelease the radio context for the UE, e.g., RNTI, 5G cell measurementconfiguration information, and DRX mode configuration information, whenthe response is received from the UE 601. After the 5G RRC connection isreleased, the UE 601 may turn off the 5G modem or perform a cell searchprocedure to search for a 5G AU.

It is obvious that the UE 601 may receive the service via the LTE systemafter turning off the 5G modem if it supports the LTE system.

As another alternative example of releasing system connection of the UE,the base station may check the buffer status of the UE 601 to determinethat no 5G radio (5G system) is necessary for serving the UE 601. Thebase station may perform the 5G RRC connection release procedure withthe S/P-GW 609 and MME 611 and transmit a 5G RRC Connection Releasemessage to the UE 601. If the 5G RRC Connection Release message isreceived, the UE 601 may release the RRC Context related to the 5G cell(base station). Meanwhile, the UE 601 may transmit a response to thebase station in response to the 5G RRC Connection Release message. Thebase station may release the 5G context (5G radio context) for the UE601. After the 5G RRC Connection is released, the UE 601 may turn offthe 5G modem or perform a cell search procedure to search for a 5G AU.

It is obvious that the UE 601 may receive the service via the LTE systemafter turning off the 5G modem if it supports the LTE system.

As another alternative example of releasing system connection of the UE,the UE 601 may transmit an RRC Connection Release Request message to thebase station, and the base station may transmit an RRC ConnectionRelease Confirm message in reply. The UE 601 may operate an RRC contextrelease timer to transmit the RRC Connection Release Request message. Ifthe 5G communication service application is deactivated, the applicationprocessor (AP) of the UE 601 may generate a command instructing releaseof the RRC connection to its 5G modem, which may transmit the RRCConnection Release Request message. If the RRC Connection ReleaseRequest message is received from the UE 601, the base station mayperform the 5G RRC Connection release procedure with the S/P-GW 609 andthe MME 611 and transmit a 5G RRC Connection Release message to the UE601. Upon receipt of the 5G RRC Connection Release message, the UE 60may release the RRC context related to the 5G cell (base station). Inresponse to the RRC Connection Release message, the UE 601 may transmita response to the base station. The base station may release the 5Gcontext (5G radio context) for the UE 601. After releasing the 5G RRCConnection, the UE 601 may turn off the 5G modem or perform a cellsearch procedure to search for a 5G AU.

According to an embodiment of the present invention, it may be possibleto configure such that the 5G UE 601 enters a DRX mode instead ofreleasing the RRC Context between the 5G UE 601 and the base stationwhen the 5G service is terminated at the UE 601. The RRC Context of the5G UE 601 may be stored in the 5G UE 601 and the base station, which usethe RRC Context at the timing when the 5G service of the 5G UE 601 isresumed. The DRX mode may be configured with an off duration that islonger than that of the DRX of the legacy 4G system and maintain the RRCcontext.

FIG. 7 is a block diagram illustrating a schematic configuration of a UEaccording to an embodiment of the present invention.

In reference to FIG. 7, the UE may include at least one processor 700and a transceiver 705.

The transceiver 705 may communicate signals with an LTE eNB and/or 5GeNB

The processor 700 may implement the operations of the UE according tothe above-described various embodiments of the present invention. Forexample, the processor 700 may include an LTE modem for LTEcommunication and a 5G modem for 5G communication.

According to an embodiment of the present invention, the processor 700may control performing of LTE data communication via the LTE eNB andreceive configuration information (e.g., RRC connection information) for5G communication from the LTE eNB and the 5G eNB. The processor 700 maycontrol reporting of a result of measurement on at least one beamformingreference signal (e.g., BMRS) received from the 5G eNB to the LTE eNB orthe 5G eNB. The processor 700 may control configuring of a 5G connectionwith the 5G eNB based on the measurement result.

FIG. 8 is a block diagram illustrating a schematic configuration of abase station according to an embodiment of the present invention. Thebase station depicted in FIG. 8 may be an LTE eNB or a 5G eNB.

As described above, the base station may include a control unit (e.g.,CU) and a radio unit (e.g., AU), and the control unit and the radio unitmay be implemented as separate devices or as a single device. In thecase that the radio unit and the control unit are implemented asseparate devices, they may be connected through an interface.

The base station may include at least one processor and a transceiver810. For example, the at least one processor may include a control unit800 and a radio unit 805. The control unit 800 and the radio unit 805may be connected to different transceivers.

The transceiver 810 may communicate signals with a UE through a radiocommunication link (LTE or 5G) and communicate signals with another basestation or device through a wired link.

The processor may implement the operations of the base station accordingto the above-described various embodiments of the present invention.

If the base station is an LTE eNB, the processor may control performingof LTE-based data communication with a UE connected through LTE. Theprocessor may control transmitting of configuration information (e.g.,RRC connection information) for 5G connection. The processor may controlreceiving of a measurement result from the UE, the measurement beingperformed on at least one beamforming reference signal transmitted fromthe 5G base station to the UE based on the configuration information.

For example, if the base station is a 5G eNB, the processor may controltransmitting of configuration information (e.g., RRC connectioninformation) for 5G connection to the UE that performs LTE datacommunication with the LTE eNB. The processor may control receiving ofthe result of a measurement performed on at least one beamformingreference signal based on the configuration information. The processormay control configuring of a second radio communication link to the UEbased on the measurement result.

FIG. 9 is a block diagram illustrating an internal device 900 of a UEthat turns on a 5G modem based on the 5G application list information inFIG. 3A of the present invention. For example, the internal device 900may include the processor 700 of FIG. 7.

A 5G App Whitelist Manager 901 manages a 5G application name list. The5G application name list may be stored in the manufacturing phase of theUE or received from the LTE/5G eNB or network through signaling. TheApplication Manager 902 may monitor the 4G and 5G applications 903 and904 that are currently running in the UE. The Application manager 902may determine whether the applications 903 and 904 running in the UE areincluded in the 5G application name list stored in the 5G App whitelistmanager. If the applications 903 and 904 running in the UE are includedin the 5G application name list, the Application manager 902 may sendthe 5G API 906 a signal for activating the 5G modem 908. If a 4Gapplication is running, the Application manager 902 may send the 4G API905 a signal for activating the 4G modem 907. The 4G API 905 maygenerate an ON/OFF command to the 4G modem 907 according to the signalfrom the application manager 902.

FIG. 10 is a diagram for explaining an operation for a 5G application toturn on a 5G modem according to an embodiment of the present invention.If the 5G application 1001 is executed, it may generate a signal to the5G API 1002 and then the 5G API 1002 may generate an ON/OFF command tothe 5G Modem 1003.

Hereinafter, a description is made of the method for a master eNB thatoperates a macro cell to add a secondary cell, e.g., millimeter wave(mmWave) cell or a cell operating at a frequency higher than LTEfrequency, to the UE according to various embodiments of the presentinvention. However, the secondary cell is not limited to theaforementioned cells. In the following description, the secondary cellmay be interchangeably referred to as secondary carrier, mmWave cell,mmWave carrier, and high frequency cell.

In the following description, although referred to as an mmWave cell,the secondary cell has the capability as follows. A secondary cell eNBmay operate on an LTE frequency, mmWave frequency, or a frequency in aband higher or lower than the LTE band. The secondary cell eNB may be abase station of a cellular technology or Wi-Fi/wigig technology. Thesecondary cell eNB may have the same capability as that of a macro celleNB. The secondary cell eNB may perform the operation of part of thefunctions of a normal eNB (e.g., user plane packettransmission/reception without RRC function). Alternatively, thesecondary cell eNB may have a functionality smaller than that of themacro cell eNB. For example, the secondary cell eNB may become atransmitting device or a transmission/reception point (TRP) or have onlythe PHY layer or the PHY layer and MAC sublayer. For example, thesecondary cell eNB may have a connection to a gateway. Alternatively,the secondary cell eNB may have no connection to a gateway. In thefollowing description, the eNB having the above characteristics may beinterchangeably referred to as a high frequency (HF) BS, mmWave celleNB, and secondary eNB (SeNB).

Various embodiments of the present invention may be considered when asecondary cell is located within the coverage of a macro cell. Forexample, at least one low frequency eNB becomes a master eNB, andmultiple mmW cells may form a secondary cell cluster.

In this situation, the RRC connected mode operation is performed asfollows. First, the UE connects to a low frequency eNB (master eNB). Thelow frequency eNB may add a secondary cell (e.g., mmW cell) to meet therequirements for a large volume of data. Since the RRC is anchored tothe low frequency eNB, the UE may avoid handover failure even whenfailing to transmit a handover signal on the secondary carrier (mmWcarrier). The UE in the idle mode may perform cell selection and monitorthe low frequency for a paging message. The system information andpaging signal may be transmitted through the macro cell but not throughthe secondary cell.

FIG. 11 is a diagram illustrating a situation where a UE located withina coverage of the master eNB is connected to the master eNB and asecondary eNB according to an embodiment of the present invention.

In reference to FIG. 11, a low frequency (LF) eNB 1100 may become theaccess point of control information, and a UE 1115 may connect tosecondary eNBs 1105 and 1110 for high data rate data communication. TheLF eNB 1100 may perform low volume data communication with the UE 1115.The low frequency is characterized by a low pathloss in comparison witha high frequency; thus, the coverage of the LF eNB 1110 may include thecoverage of the small size high frequency cell. The UE 1115 may at leastconnect to the LF eNB 1100 and may have two or more connections:connection via the LF eNB 1100 and connections via the high frequencyeNBs 1105 and 1110.

In order to add a secondary cell to the UE, the UE may perform secondarycell search and measurement and determine whether to add the secondarycell based on the search and measurement result. According to which onetriggers the secondary cell search and measurement and how the secondarycell search and measurement are triggered, various embodiments may bediscussed.

1) Macro eNB (e.g., LF eNB) Initiated Triggering after ConnectionRequest from UE

FIG. 12 is a signal flow diagram illustrating a procedure where a macroeNB triggers secondary cell search and measurement based on UE contextreceived from an MME after a UE has requested to the macro eNB forconnection.

At step 1215, the UE 1200 may transmit a connection request to the macrocell (e.g., LF cell). According to the EPS core network operation, theMME 1210 may establish an EPS bearer with an appropriate QoS parameterbased on the subscription information of the UE 1200. At step 1220, theEPS bearer information related to the corresponding UE may betransmitted, in the state of being contained in UE context, to the macroeNB 1205 to which the UE has requested for connection.

First, the macro eNB 1205 may determine whether there is a mmWave cellthat it can control and which can be used for the UE 1200. Second, themacro eNB 1205 may determine whether the EPS bearer has a QoS factor forhigh data rate data based on the UE context received from the MME 1210.Third, the macro eNB 1205 may determine whether the UE has thecapability of operating in the high frequency band. The UE capabilityinformation may be acquired from the connection request transmitted tothe macro eNB at step 1215 or by inquiring to the low frequency eNB1205. The aforementioned three conditions may be tested in sequence orsimultaneously.

If all of the three conditions are fulfilled, the macro eNB 1205 maytrigger high frequency cell search at step 1225. For example, the macroeNB 1205 may request to the UE 1200 for high frequency operationcapability, and the UE 1200 may reply to the request.

The macro eNB 1205 may transmit a high frequency cell measurementconfiguration (e.g., mmWave config) to the UE 1200 at step 1230. Themeasurement configuration may be broadcast through a broadcast channelor transmitted through a UE-specific channel.

The UE 1200 may perform high frequency cell (e.g., mmWave cell) searchand measurement at step 1235. If a predetermined event occurs, the UEmay report the measurement result to the macro eNB 1205 at step 1240.The macro eNB may determine at step 1245 whether to add at least onehigh frequency cell for the UE based on the measurement result.

2) Macro eNB (e.g., LF eNB) Initiated Triggering Upon Detection ofDownlink Data Occurrence after Connection

FIG. 13 is a signal flow diagram illustrating a procedure where a macroeNB triggers secondary cell search and measurement based on apredetermined type of data from the network after a UE has connected tothe macro eNB.

At step 1315, the UE 1300 is already in the RRC connected state with themacro eNB 1305.

If downlink data traffic occurs afterward in a server (not shown) of thenetwork 1310, the macro eNB 1305 may receive the data from the network1310 at step 1320. The data may be a predetermined type of data, e.g.,high data rate data.

The macro eNB 1305 may determine at step 1325 whether the data is apredetermined type of data, e.g., high data rate data, based on areceived factor of EPS bearer or an indicator indicative of high datarate data that an MME or a gateway transmits along with data traffic.

At step 1330, the macro eNB 1305 may trigger secondary cell search,e.g., high frequency cell search, when the data amount accumulated in abuffer is equal to or greater than a predetermined size. Optionally, themacro eNB 1305 may inquire to the UE 1300 about the high frequencyoperation capability and start the search. Here, the high frequencyoperation capability information may be acquired from RRC connectionrequests transmitted to the macro eNB 1305 or by inquiring to the UE1300 after receiving the high data rate data from the network.

Afterward, the macro eNB 1305 may transmit high frequency cellmeasurement configuration (e.g., mmWave config) to the UE 1300 at step1335. The measurement configuration may be broadcast through a broadcastchannel or transmitted through a UE-specific channel.

The UE 1300 may perform high frequency cell (e.g., mmWave cell) searchand measurement at step 1340. The UE 1300 may report the measurementresult to the macro eNB 1305 at step 1345. The macro eNB 1305 maydetermine at step 1350 whether to add at least one high frequency cellfor the UE based on the measurement result.

After the high frequency cell is added for the UE 1300, high data ratedata is transmitted via the SeNB that controls the high frequency cell.That is, if no high data rate data is received from the network 1310over a predetermined time or a high data rate data hold indicator isgiven to the UE 1300, the macro eNB 1305 may release or deactivate theSeNB. If the SeNB has already been added but in the deactivated stateand, in this state, if high data rate data occurs again, the macro eNB1305 may activate the SeNB without adding an extra SeNB.

3) Macro eNB (e.g., LF eNB) Initiated Triggering Upon Detection ofUplink Data Occurrence after Connection

FIG. 14 is a signal flow diagram illustrating a procedure where a macroeNB triggers secondary cell search and measurement based on apredetermined type of uplink data from a UE connected to the macro eNB.

At step 1410, the UE 1400 may be in the RRC Connected state with themacro eNB 1405.

At step 1415, the UE 1400 may detect occurrence of a predetermined typeof data, e.g., high data rate data, from the application layer. If ahigh data rate service or application is executed, the UE 1400 mayregard this as the occurrence of high data rate data. If the uplink dataaccumulated in the buffer of the UE 1400 is greater than a predeterminedamount, this may mean an occurrence of high data rate data.

At step 1420, the UE 1400 may transmit to the macro eNB 1405 a messageindicating the predetermined type of data, e.g., high data rate dataindication message. The predetermined data type may be indicated bytransmitting logical channel information in the buffer status report(BSR) or an indicator in a MAC CE. It may also be possible to transmit adifferent service type indicator. The service type indicator isdescribed later in detail.

Optionally, the macro eNB 1405 may inquire to the UE 1400 about highfrequency cell capability. This information may be acquired from the RRCConnection request.

If the UE has the high frequency operation capability, the macro eNB1405 may trigger secondary cell (e.g., high frequency cell) search atstep 1425. At step 1430, the macro eNB 1405 may transmit measurementconfiguration (e.g., mmWave config) for high frequency cell search tothe UE 1400. The measurement configuration may be broadcast through abroadcast channel or transmitted through a UE-specific channel.

At step 1435, the UE 1400 may search for a high frequency cell (e.g.,mmWave cell) and perform measurement. At step 1440, the UE 1400 mayreport a measurement result to the macro eNB 1405. At step 1445, themacro eNB 1405 may determine to add at least one high frequency cell forthe UE based on the measurement result.

After the high frequency cell is added, the high data rate data istransmitted via the SeNB and, if the high data rate data occurrencestops, the SeNB may be released or deactivated. The UE 1400 may transmitto the macro eNB 1405 an indicator indicating that the high data ratedata occurrence has stopped. If the SeNB has already been added but inthe deactivated state and, in this state, if high data rate data occursagain, the macro eNB 1405 may activate the SeNB without adding an extraSeNB.

4) UE Initiated Triggering Upon Detection of Uplink Data Occurrenceafter Connection

FIG. 15 is a signal flow diagram illustrating a procedure where a UEtriggers secondary cell search and measurement based on a predeterminedtype of uplink data occurring at the UE after being connected to a macroeNB.

At step 1510, the UE 1500 may already be in the RRC connected state withthe macro eNB 1505 at step 1510.

At step 1515, the UE 1500 may detect occurrence of a predetermined typeof data, e.g., high data rate data, from the application layer. If ahigh data rate service or application is executed, the UE 1500 mayregard this as the occurrence of high data rate data. If the uplink dataamount accumulated in the buffer of the UE 1500 is greater than apredetermined amount, this may mean occurrence of high data rate data.

If the UE 1500 detects the occurrence of the high data rate data, it mayperform high frequency cell (e.g., mmWave cell) search and measurementat step 1520. The high frequency measurement configuration (e.g., mmWaveconfig) may be received from the macro eNB 1505 in advance. Themeasurement configuration may be broadcast through a broadcast channelor transmitted through a UE-specific channel.

At step 1525, the UE 1500 may report the measurement result to the macroeNB 1505. At step 1530, the macro eNB 1505 may determine to add at leastone high frequency cell based on the measurement result.

After the high frequency cell is added, the high data rate data istransmitted via the SeNB and, if the high data rate data occurrencestops, the SeNB may be released or deactivated. The UE 1500 may transmitto the macro eNB 1505 an indicator indicating that the high data ratedata occurrence has stopped. If the uplink data buffered in the uplinkdata buffer of the UE 1500 is less than a predetermined amount, the UE1500 may determine that the high data rate data occurrence has stopped.If the SeNB has already been added but in the deactivated state and, inthis state, if high data rate data occurs again, the macro eNB 1505 mayactivate the SeNB without adding an extra SeNB.

5) UE Initiated Triggering Upon Detection of Uplink Data Occurrence inIdle State

FIG. 16 is signal flow diagram illustrating a procedure where a UEtriggers secondary cell search and measurement based on a predeterminedtype of uplink data occurring at the UE in the idle state.

This embodiment is directed to the case where the UE 1600 is in the idlestate.

At step 1610, the macro eNB 1605 may continue broadcasting measurementconfiguration (e.g., mmWave config) for high frequency cell search andmeasurement to the UE 1600 through a broadcast channel while the UE 1600stays in the idle state as denoted by reference number 1615.

At step 1620, the UE 1600 may detect occurrence of a predetermined typeof data, e.g., high data rate data, from the application layer. If ahigh data rate service or application is executed, the UE 1600 mayregard this as the occurrence of high data rate data. If the uplink dataamount accumulated in the buffer of the UE 1600 is greater than apredetermined amount, this may also mean occurrence of high data ratedata.

If the UE detects the occurrence of the high data rate data, it mayperform high frequency cell (e.g., mmWave cell) search and measurementat step 1625.

At step 1630, the UE 1600 may report the measurement result to the macroeNB 1505. In this embodiment, the measurement result may be conveyed inthe connection request message that is transmitted from the UE 1600 tothe macro eNB 1605.

Upon receipt of the connection request, the network entities (MIME, HSS,S-GW, P-GW, etc.) may cooperate to establish an RRC connection. That is,as an operation of the EPS core network, the MME may generate an EPSbearer with an appropriate QoS parameter based on the subscriptioninformation of the UE. The information on the EPS bearer established forthe UE 1600 may be transmitted to the eNB 1605 to which the UE 1600 hasrequested for access. The macro eNB 1605 may identify the presence ofthe high frequency cell based on the measurement result and determine atstep 1635 to add at least one high frequency cell.

After the high frequency cell is added, the high data rate data istransmitted via the SeNB and, if the high data rate data occurrencestops, the SeNB may be released or deactivated. The UE 1600 may transmitto the macro eNB 1605 an indicator indicating that the high data ratedata occurrence has stopped. If the uplink data buffered in the uplinkdata buffer of the UE 1600 is less than a predetermined amount, the UE1600 may determine that the high data rate data occurrence has stopped.If the SeNB has already been added but in the deactivated state and, inthis state, if high data rate data occurs again, the macro eNB 1605 mayactivate the SeNB without adding an extra SeNB.

6) UE Initiated Triggering Upon Detection of Downlink Data Occurrence inIdle State

FIG. 17 is a signal flow diagram illustrating a procedure where a UE inthe idle state triggers secondary cell search and measurement based on apaging message indicative of the presence of downlink data.

This embodiment is directed to the case where the UE 1700 is in the idlestate.

At step 1715, the macro eNB 1705 may continue broadcasting measurementconfiguration (e.g., mmWave config) for high frequency cell search andmeasurement to the UE 1600 through a broadcast channel.

In this situation, if a predetermined type of data, e.g., high data ratedata, occurs afterward in a server (not shown) of the network, the MIME1710 may transmit to the macro eNB 1705 at step 1720 a paging messageincluding an indicator indicative of a predetermined service type. Ifthe service type is set to high data rate data, the macro eNB 1705transmits an RRC paging message including an indicator set to high datarate data to the UE 1700 through PDCCH at step 1725.

Here, the high data rate data indicator included in the RRC pagingmessage may be a 1-bit indicator. In the case that the RRC pagingmessage includes a service type indicator, the service type indicatormay be used to indicate a service type based on legacy QoS informationsuch as QCI and ARP of the EPS bearer or to contain indicationinformation according to a mapping rule specified in the standardspecification.

Meanwhile, the RRC paging message may include at least one of pagingrecord, UE identity, core network domain information, system informationmodification, ETWS indication, and service type indication.

Upon receipt of the RRC paging message, the UE 1700 may perform highfrequency cell (e.g., mmWave cell) search and measurement at step 1730according to the previously received measurement configuration.

At step 1735, the UE 1700 may report the measurement result to the macroeNB 1705. In this embodiment, the measurement result may be conveyed inthe connection request message that is transmitted from the UE 1700 tothe macro eNB 1705.

Upon receipt of the connection request, the network entities (MME, HSS,S-GW, P-GW, etc.) may operate to establish an RRC connection. That is,as an operation of the EPS core network, the MME may generate an EPSbearer with an appropriate QoS parameter based on the subscriptioninformation of the UE. The information on the EPS bearer established forthe UE 1700 may be transmitted to the eNB 1705 to which the UE 1700 hasrequested for access. The macro eNB 1705 may identify the presence ofthe high frequency cell based on the measurement result and determine atstep 1740 to add at least one high frequency cell.

After the high frequency cell is added, the high data rate data istransmitted via the SeNB and, if the high data rate data occurrencestops, the SeNB may be released or deactivated. The UE 1700 may transmitto the macro eNB 1705 an indicator indicating that the high data ratedata occurrence has stopped. If the uplink data buffered in the uplinkdata buffer of the UE 1700 is less than a predetermined amount, the UE1700 may determine that the high data rate data occurrence has stopped.If the SeNB has already been added but in the deactivated state and, inthis state, if high data rate data occurs again, the macro eNB 1705 mayactivate the SeNB without adding an extra SeNB.

FIG. 18 is a signal flow diagram illustrating a procedure for a UE inthe idle state to trigger a multiple secondary cell search procedure andmeasurement based on a paging message indicative of the presence ofdownlink data according to an embodiment of the present invention.

A description is made hereinafter with reference to FIG. 18 of theprocedure of adding multiple SeNBs. Although it is expressed in FIG. 18that multiple SeNBs are added, this may be interpreted as meaning thatmultiple secondary cells are added.

At step 1812, the MeNB (e.g., LF eNB) 1802 may broadcast predeterminedfrequency band measurement configuration with an ID indicative of apredetermined service type to the UE 1800. At step 1814, the UE 1800 maybe staying in the idle state. At step 1816, the MME 1810 may transmit apaging message with a service type ID to the MeNB 1802. At step 1818,the MeNB 1802 may notify the UE 1800 of the resource position of thepaging message using PDCCH with P-RNTI and transmit an RRC pagingmessage to the UE 1800 at step 1820.

The UE 1800 may receive the paging message on the resource indicatedwith the P-RNTI in the PDCCH. At step 1824, the UE 1800 may compare theservice type ID including the paging message and the service type IDgiven in the previous measurement configuration to retrieve themeasurement configuration information mapped to the service type ID andperform channel search and measurement on the frequency corresponding tothe service type ID. On the frequency corresponding to the service typeID, SeNB1 1804, SeNB2 1806, and SeNB3 1808 may be found; thus, at step1822, channel measurement may be performed for SeNB1 1804, SeNB2 1806,and SeNB3 1808.

At step 1826, the UE 1800 may transmit a random-access channel (RACH) tothe MeNB 1802. At step 1828, the UE 800 may transmit a connectionrequest message including the measurement result to the MeNB 1802 inresponse to the RACH. The RACH is transmitted to the MeNB 1802 to whichthe UE connects to after wakeup from the idle state.

The MeNB 1802 may determine the signal strengths of the candidate SeNBs(e.g., SeNB1 to SeNB3) based on the received measurement results andselect target SeNBs to be grouped into an SeNB candidate cluster. Atstep 1830, the MeNB 1802 may transmit an addition request message to theSeNBs (e.g., SeNB1 and SeNB2) included in the SeNB candidate cluster.Upon receipt of the addition request message, the SeNB1 1804 and theSeNB2 1806 may determine whether to accept based on their resourceoccupancy statuses and, if it is determined to accept, transmit to theMeNB 1802 a response message including ack at step 1832.

The MeNB 1802 may determine the SeNB to be added based on the responsemessage and, at step 1836, transmit to the UE 1800 a connectionreconfiguration message including the information for adding the SeNB.For example, if it is determined to add the SeNB1 1804 and SeNB2 1806,the MeNB 1802 may transmit the reconfiguration message including theaccess-related information of the SeNB1 and SeNB2 (e.g., dedicated RACHpreamble information and access-related common or dedicated information)along with the respective SeNB IDs. The MeNB 1802 may transmit areconfiguration complete message to the SeNB1 1804 and SeNB2 1806 atstep 1838.

When the MeNB 1802 performs an addition request operation in associationwith the SeNBs included in the SeNB candidate cluster, it may transmit aUE context information to the respective SeNBs. The MeNB 1802 may usethe measured signal power information included in the measurement reportinformation when designing a handover triggering event afterward. Theinformation on the event designed in this way may include an event name,an offset factor, and an event-specific threshold factor. Themeasurement configuration information related to the event may bedelivered to the UE 1800 through a connection reconfiguration message.

If the connection reconfiguration message is received, the UE 1800 mayuse the measurement configuration and access-related factor informationincluded in the message. In the case that the measurement configurationinformation is received, if a preconfigured event occurs, the UE 1800may perform a predefined operation that is supposed to be triggered bythe event. In the case where the access-related factor information isreceived, the UE 1800 may perform access to the corresponding cell usingthis information.

Upon receipt of the connection reconfiguration message, the UE 1800 maytransmit a connection setup complete message to the MeNB 1802 at step1840. The MeNB 1802 may transmit an initial UE message and/or servicerequest message to the MME 1810 at step 1842.

The UE 1800 may perform a RACH procedure with the SeNB1 1804 and SeNB21806 at step 1844 to achieve synchronization and, afterward, performdata communication with the SeNB1 1804 and SeNB2 1806.

7) eNB Initiated Triggering Upon Detection of Uplink Data Occurrence inIdle State

FIG. 19 is a signal flow diagram illustrating a procedure where an eNBtriggers secondary cell search and measurement based on the presence ofuplink data from a UE in the idle state.

This embodiment is directed to the case where the UE 1600 is in the idlestate as denoted by reference number 1910.

At step 1915, the UE may detect occurrence of a predetermined type ofdata, e.g., high data rate data, from the application layer. If a highdata rate service or application is executed, the UE 1900 may regardthis as the occurrence of high data rate data. If the uplink data amountaccumulated in the buffer of the UE 1900 is greater than a predeterminedamount, this may also mean occurrence of high data rate data.

At step 1920, the UE 1900 may transmit to the macro eNB 1905 aconnection request message including a high data rate data indicator.

The macro eNB 1905 may determine whether the UE 1900 has high frequencyoperation capability based on the UE information conveyed in theconnection request message. It may also be possible to inquire to the UE1900 about its high frequency operation capability. If it is determinedthat the UE 1900 has high frequency operation capability, the macro eNB1905 may trigger a high frequency cell search operation at step 1925 andtransmit measurement configuration (e.g., mmWaveConfig) to the UE 1900at step 1930. The measurement configuration may be broadcast through abroadcast channel or transmitted through a UE-specific channel.

At step 1935, the UE 1900 may perform high frequency cell (e.g., mmWavecell) search and measurement based on the received measurementconfiguration.

At step 1940, the UE 1900 may report the measurement result to the macroeNB 1905. The macro eNB 1905 may determine to add at least one highfrequency cell for the UE based on the received measurement result.

FIG. 20 is a diagram for explaining a high frequency cell (e.g., mmWavecell) search and measurement method based on beamforming according to anembodiment of the present invention.

A signal broadcast through a high frequency cell for use in cell searchand measurement may be transmitted at a predetermined interval 2005during a transmission period 2010 determined based on a predeterminedoffset value. This signal may be transmitted using TX beam sweeping orreceived using RX beam sweeping. For example, the UE may performmeasurement on the signal by sweeping the TX beam in the state of fixingthe RX beam in sequence as shown in part (a) as denoted by referencenumber 2015 and sweeping the RX beam in the state of fixing the TX beamin sequence as shown in part (b) as denoted by reference number 2020.

According to an embodiment of the present invention, the measurementconfiguration (e.g., mmWaveConfig) transmitted from the macro eNB to theUE may include a mmW signal transmission period, a mmW signaltransmission start offset, and mmW signal transmission time information.This information indicates a downlink transmission timing of the macroeNB.

The measurement configuration may include beamforming information. Forexample, the measurement configuration may include at least one of anumber of TX beams of the high frequency cell, high frequency signaltime slot information per TX beam, an order of TX beam sweeping, anumber of repetitions of a TX beam before transmission of the next TXbeam, and beam ID information. The measurement configuration may alsoinclude at least one of monitoring-target cell list information, cellmonitoring order information, and measurement gap information determinedconsidering a high frequency signal transmission period.

The measurement configuration may also include intra-/inter-frequencyneighboring cell, particularly different RAT, information (UMTS, GSM,CDMA2000, HRPD, and 1×RTT information). The measurement configurationmay also include criteria for an event triggering measurement report ofthe UE and quantity information. The measurement configuration may alsoinclude information mapping a measurement target and a measurementconfiguration as a measurement identifier. The measurement configurationmay also include measurement quantity for use in assessing all eventsand related filtering information and RAT information for use inreporting a measurement result. The measurement configuration may alsoinclude information on the measurement gap with the current macro eNBfor other measurement targets.

According to an embodiment of the present invention, the measurementreport that the UE transmits to the macro eNB may include a measurementID, a cell ID, a measurement beam ID, and a measurement result(reference signal received power (RSRP), reference signal receivedquality (RSRQ), and received signal code power (RSCP), and energy tonoise ratio).

FIG. 21 is a block diagram illustrating a schematic configuration of aUE according to an embodiment of the present invention.

The UE may include at least one processor 2100 and a transceiver 2105.

The transceiver 2105 may communicate signals with other devices (e.g.,MeNB and SeNB) under the control of the processor 2100.

According to various embodiments of the present invention, the processor2100 may control the operations of the UE as described with reference toFIGS. 12 to 19. For example, the processor 2100 may include an LTE modemfor LTE communication and a 5G modem for 5G communication.

FIG. 22 is a block diagram illustrating a schematic configuration of aneNB according to an embodiment of the present invention. The eNBconfigured as shown in FIG. 22 may be an LTE eNB (low frequency eNB andmaster eNB) or a 5G eNB (high frequency eNB and secondary cell eNB).

The eNB may include a processor 2200 and a transceiver 2205.

The transceiver 2205 may communicate signals with a UE through a radiocommunication link (LTE or 5G) and communicate signals with another eNBor device through a wired link under the control of the processor 2200.

According to various embodiments of the present invention, the processor2200 may control the operations of the eNB (LTE eNB or 5G eNB) asdescribed with reference to FIGS. 12 to 19. The above-describedoperations of the eNB and UE may be realized with a memory storingcorresponding program codes inside an arbitrary component of the eNB orUE. That is, the controller of the eNB or the UE may execute theabove-described operations by reading out the program codes stored inthe memory device by means of a processor or a central processing unit(CPU).

The various components, modules composing an entity, an eNB, or a UE maybe implemented in the form of a hardware circuit such as a complementarymetal oxide semiconductor-based logic circuit, firmware, software and/ora combination of hardware and firmware, and/or a software element storedin a machine-readably medium. For example, various electrical structureand methods may be executed by means of electric circuits such astransistors, logic gates, and on-demand semiconductors.

Although the description has been made with reference to particularembodiments, the present invention can be implemented with variousmodifications without departing from the scope of the present invention.Thus, the present invention is not limited to the particular embodimentsdisclosed, and it will include the following claims and theirequivalents.

The invention claimed is:
 1. A method performed by a terminal in awireless communication system, the method comprising: receiving, from afirst base station, a first message requesting a capability of theterminal for a radio access technology type, the radio access technologytype includes new radio (NR), and a dual connectivity of evolveduniversal terrestrial radio access (E-UTRA) and the NR; andtransmitting, to the first base station, a second message includingfirst information on the capability of the terminal for the NR andsecond information on the capability of the terminal for the dualconnectivity, wherein the second message further includes first bandcombinations that the terminal supports for the NR and second bandcombinations that the terminal supports for the dual connectivity. 2.The method of claim 1, further comprising: receiving, from the firstbase station, a third message configuring a radio resource control (RRC)connection with a second base station; and communicating with the secondbase station based on the third message, wherein the first base stationis a master base station of the dual connectivity and the second basestation is a secondary base station of the dual connectivity.
 3. Themethod of claim 2, wherein the first base station supports the E-UTRA,and wherein the second base station supports the NR.
 4. A methodperformed by a first base station in a wireless communication system,the method comprising: transmitting, to a terminal, a first messagerequesting a capability of the terminal for a radio access technologytype, the radio access technology type includes new radio (NR), and adual connectivity of evolved universal terrestrial radio access(E-UTRA); and receiving, from the terminal, a second message includingfirst information on the capability of the terminal for the NR andsecond information on the capability of the terminal for the dualconnectivity, wherein the second message further includes first bandcombinations that the terminal supports for the NR and second bandcombinations that the terminal supports for the dual connectivity. 5.The method of claim 4, further comprising: transmitting, to theterminal, a third message configuring a radio resource control (RRC)connection with a second base station, wherein the terminal is connectedwith the second base station based on the third message, and wherein thefirst base station which is a master base station of the dualconnectivity and the second base station is a secondary base station ofthe dual connectivity.
 6. The method of claim 5, wherein the first basestation supports the E-UTRA, and wherein the second base stationsupports the NR.
 7. A terminal in a wireless communication system, theterminal comprising: a transceiver; and at least one processorconfigured to: control the transceiver to receive, from a first basestation, a first message requesting a capability of the terminal for aradio access technology type, the radio access technology type includesnew radio (NR), and a dual connectivity of evolved universal terrestrialradio access (E-UTRA) and the NR, and control the transceiver totransmit, to the first base station, a second message including firstinformation on the capability of the terminal for the NR and secondinformation on the capability of the terminal for the dual connectivity,wherein the second message further includes first band combinations thatthe terminal supports for the NR and second band combinations that theterminal supports for the dual connectivity.
 8. The terminal of claim 7,wherein the at least one processor is further configured to: control thetransceiver to receive, from the first base station, a third messageconfiguring a radio resource control (RRC) connection with a second basestation, and communicate with the second base station based on the thirdmessage, and wherein the first base station is a master base station ofthe dual connectivity and the second base station is a secondary basestation of the dual connectivity.
 9. The terminal of claim 8, whereinthe first base station supports the E-UTRA, and wherein the second basestation supports the NR.
 10. A first base station in a wirelesscommunication system, the base station comprising: a transceiver; and atleast one processor configured to: control the transceiver to transmit,to a terminal, a first message requesting a capability of the terminalfor a radio access technology type, the radio access technology typeincludes new radio (NR), and a dual connectivity of evolved universalterrestrial radio access (E-UTRA) and the NR, and control thetransceiver to receive, from the terminal, a second message includingfirst information on the capability of the terminal for the NR andsecond information on the capability of the terminal for the dualconnectivity, wherein the second message further includes first bandcombinations that the terminal supports for the NR and second bandcombinations that the terminal supports for the dual connectivity. 11.The base station of claim 10, wherein the at least one processor isfurther configured to control the transceiver to transmit, to theterminal, a third message configuring a radio resource control (RRC)connection with a second base station, wherein the terminal is connectedwith the second base station based on the third message, and wherein thefirst base station which is a master base station of the dualconnectivity and the second base station is a secondary base station ofthe dual connectivity.
 12. The base station of claim 11, wherein thefirst base station supports the E-UTRA, and wherein the second basestation supports the NR.